Conventionally, in a process of correcting the dynamic range for reproducing detailed information of input image data, there is an LPF process for generating a low-frequency component of an image with an LPF (Low Pass Filter), which is a filter that allows only a low-frequency signal to pass therethrough. The LPF process for generating a low-frequency component from input image data is hard to improve the processing speed because the LPF is large in filter size and the processing load is heavy.
To cope with this problem, recently, technologies for preventing the processing delay in an LPF process have been disclosed. For example, in a technology disclosed in Japanese Laid-open Patent Publication No. 2004-221645, as illustrated in FIG. 11, by performing a low-frequency-component generating process using a reduced image of a previous frame, the processing load is spread, and the processing delay in an LPF process can be prevented.
Specifically, in the technology disclosed in Japanese Laid-open Patent Publication No. 2004-221645, when image data of the N-th frame is received, a low-frequency component is generated from the received N-th frame, and a dynamic-range correction process of the (N+1)-th frame is performed by using the generated low-frequency component of the N-th frame. Namely, in the technology disclosed in Japanese Laid-open Patent Publication No. 2004-221645, the dynamic-range correction process of the (N+1)-th frame is performed by using the low-frequency component of the N-th frame, and dynamic-range correction of the (N+2)-th frame is performed by using a low-frequency component of the (N+1)-th frame; such a process is repeated.
However, the conventional technology described above has a problem that the processing delay occurs. Specifically, if an LPF process is not completed within a time taken to generate a low-frequency component of a previous frame, the processing delay occurs because a subsequent process cannot be performed until the LPF process is completed.